In the drilling and production of oi and gas wells it is frequently necessary to penetrate one or more production zones to reach an underlying zone with production tubing. Each production zone is served by its own string of production tubing which then must penetrate the overlying production zones to reac the surface. At the point where each string of production tubing penetrates an overlying production zone, the tubing can be subjected to severe erosion.
Particularly where the production zone being penetrated produces high pressure gas, abrasive materials entrained in the gas can quickly erode the surface of the production tubing penetrating that zone. High pressure gas moves at very high velocities when the zone is producing and it can contain such entrained erosive materials as grains of sand or drops of liquid. Where the high velocity gas enters the well bore, it impinges upon the penetrating production tubing from an underlying zone and, depending upon the material from which the production tubing is made, the high velocity gas can quickly damage or even penetrate the wall of the production tubing.
When the wall of the production tubing has been penetrated in an overlying zone, communication is established between two different production zones through the failed production tubing string. Communication between zones can be highly undesirable, and isolation between the zones must be maintained. Isolation between the zones in the well bore is generally obtained by the use of packers about the production tubing between production zones. When erosion of production tubing has reached an advanced state it becomes necessary to replace the eroded section or sections of tubing. This requires removing the production tubing string from the well bore, replacement of the failed joints of tubing and reinsertion of the tubing string into the well bore along with any necessary replacement of packers.
Different tubing materials will erode at different rates and to different degrees depending upon the velocity of the impinging fluid as well as the type and amount of abrasive materials entrained in the fluid. Some materials are considered highly erosion resistant, and various methods have been used to incorporate these materials into the design of the production tubing where the tubing must penetrate overlying producing zones. Joints of pipe or tubing have been designed which incorporate a jacket of a highly erosion resistant material such as tungsten carbide over the production tubing. Various methods are used to insure that the tungsten carbide will surround the tubing at the areas where the high velocity fluid enters the well bore. The tungsten carbide is generally installed in stacks of relatively short rings and held in place longitudinally by various types of sleeves and collars. In some designs the rings are kept pressed together by the installation of a spring, such as a coil spring, around the tubing to press against the end of one of the tungsten carbide rings.
A major problem with the use of a highly erosion resistant material, such as tungsten carbide, is that such materials, while being very hard, are also very brittle and therefore subject to damage when placed under radial or axial loads. When making up a tubing string for insertion into a well, it is necessary to support the top joint on the string at the well head and to hold that joint against rotation while threading it to the next joint to be installed on the string. Power tongs or similar tools are normally used to hold one joint against rotation while rotating the next joint being installed in order to thread the two joints together. Such power equipment necessarily bites into the surface of the tubing joint in order to apply the necessary torque to either hold the joint against rotation or to rotate the joint in making up the thread. If such power tools are used on a surface of the blast joint where the erosion resistant material, such as tungsten carbide, is exposed, the torque is not efficiently transferred to the tubing and the tungsten carbide rings can easily become chipped and cracked, resulting in a loss of protection against abrasion once placed into service in a production zone.
Another operation frequently encountered which can result in damage to the tungsten carbide rings is the gripping of a blast joint from above with pipe slips having upwardly canted internal teeth. These teeth must necessarily dig into the surface of the joint to achieve their gripping action in order to pull the blast joint or other piece of equipment out of the well bore. Gripping of a blast joint by such a slip, if the slip teeth contact the tungsten carbide rings, can result in cracking or breaking of the rings as mentioned before in the case of power tongs, by the application of radial or axial forces, through the slip teeth.
Some blast joints, using tungsten carbide rings, incorporate thin metal sleeves on the outside of the tungsten carbide rings, but these sleeves are of insufficient strength to withstand the radial and axial stresses imparted by power tools, and the sleeves typically are not mounted to the inner production tubing with sufficient mechanical strength to transfer the necessary torque or axial force to the tubing itself. These thin sleeves are generally only effective at protecting the tungsten carbide rings during assembly and handling which does not involved the use of the aforementioned power tools.
Presently known blast joints, therefore, in addition to being very expensive, re somewhat fragile, and they cannot be installed in a string of production tubing as if they were simply another joint of production tubing. It is desirable to design a blast joint which provides protection against erosion for its full length without any gaps, but which can be handled by the use of power tongs and pipe slips without any unusual degradation of the joint. It is further desirable to design such a blast joint which can be threaded into place in a production tubing string as if it were simply another joint of production tubing, either as a single joint or as a string of consecutive joints having a continuous protective sheath of tungsten carbide rings without any gaps in between.